1. Field of the Invention
The present invention relates to phenolic emulsions. More particularly, the present invention relates to resole phenolic resin in water emulsions containing an anti-migratory agent which are used to impregnate cellulosic substrates.
2. Description of the Prior Art
Emulsified phenolics are well known to the prior art and have been recommended for use in the paper industry for impregnating substrates and for use as beater additives for a variety of end uses.
When substantially water based phenolics, i.e., either liquid phenolic resoles or emulsified (in water) phenolic resins are used for the impregnation of paper, there is experienced, during a drying operation after paper treatment, a phenomenon known as migration. Thus, the resin tends to physically move from center regions of a paper sheet to surface regions thereof (i.e. a treated sheet's opposed faces). Thus, in a product sheet member from which volatiles have been removed, the resin tends to be concentrated at or near treated sheet surfaces. Heretofore, this problem has been partially solved by the use of solvent based phenolic resins.
While, for some purposes, resin migration is desirable since there are benefits sometimes achieved by having the phenolic resin near treated paper surfaces, for many purposes, the phenomenon of resin migration presents severe industrial problems since the product treated sheet has a non-uniform resin distribution. For example, resin migration causes loss of strength, reduction in porosity, embrittlement (e.g. poor pleatability), etc. The art, then, has long sought ways of minimizing and even eliminating migration in sheet members treated with emulsifiable phenolic resins.
There has now been discovered a system for minimizing and even substantially eliminating phenolic resin migration in porous woven or non-woven sheet members treated with emulsifiable water based phenolics. Not only does the system of this invention reduce or eliminate phenolic resin migration in treated sheet members, but also the product treated sheet members display surprising improvement in strength, porosity, and flexibility. This new composition of matter results in a very low degree of migration that is unattainable with any known water based system and even the previously mentioned solvent based phenolics. In addition, the system does not suffer from the economic and ecological drawbacks inherent in the use of a solvent based phenolic.
These new compositions of matter are especially useful as impregnating resins for filter paper.